Granulocyte colony stimulating factor (G-CSF) is a glycoprotein which stimulates the survival, proliferation, differentiation and function of neutrophil granulocyte progenitor cells and mature neutrophils. The two forms of recombinant human G-CSF in clinical use are potent stimulants of neutrophil granulopoiesis and have demonstrated efficacy in preventing infectious complications of some neutropenic states. They can be used to accelerate neutrophil recovery from myelosuppressive treatments.
G-CSF decreases the morbidity of cancer chemotherapy by reducing the incidence of febrile neutropenia, the morbidity of high-dose chemotherapy supported by marrow transplantation, and the incidence and duration of infection in patients with severe chronic neutropenia. Further, G-CSF has been shown to have therapeutic effect when administered after the onset of myocardial infarction.
Acute myelosuppression as a consequence of cytotoxic chemotherapy is well recognized as a dose-limiting factor in cancer treatment. Although other normal tissues may be adversely affected, bone marrow is particularly sensitive to proliferation-specific treatments such as chemotherapy and radiation therapy. For some cancer patients, hematopoietic toxicity frequently limits the opportunity for chemotherapy dose escalation. Repeated or high dose cycles of chemotherapy can lead to stem cell depletion of hematopoietic stem cells and their progeny.
Prevention of and protection from the side effects of chemotherapy and radiation therapy would be of great benefit to cancer patients. G-CSF and other growth factors have been shown to alleviate such side effects by increasing the number of normal critical target cells, particularly hematopoietic progenitor cells.
The human form of G-CSF was cloned by groups from Japan and the U.S.A. in 1986 (see e.g., Nagata et al. Nature 319: 415-418, 1986). The natural human glycoprotein exists in two forms, one of 175 and the other of 178 amino acids. The more abundant and more active 175 amino acid form has been used in the development of pharmaceutical products by recombinant DNA technology.
The recombinant human G-CSF synthesised in an E. coli expression system is called filgrastim. The structure of filgrastim differs slightly from the natural glycoprotein. The other form of recombinant human G-CSF is called lenograstim and is synthesised in Chinese hamster ovary (CHO) cells.
hG-CSF is a monomeric protein that dimerizes the G-CSF receptor by formation of a 2:2 complex of 2 G-CSF molecules and 2 receptors (Horan et al. Biochemistry, 35(15): 4886-96 (1996)). The following hG-CSF residues have been identified by X-ray crystalographic studies as being part of the receptor binding interfaces: G4, P5, A6, S7, S8, L9, P10, Q11, S12, L15, K16, E19, Q20, L108, D109, D112, T115, T116, Q119, E122, E123, and L124 (see e.g., Aritomi et al., (1999) Nature 401: 713).
The commercially available forms of rhG-CSF have a short-term pharmacological effect and must often be administered more than once a day for the duration of the leukopenic state. A molecule with a longer circulation half-life would decrease the number of administrations necessary to alleviate leukopenia and prevent consequent infections. Another problem with currently available rG-CSF products is the occurrence of dose-dependent bone pain. Since bone pain is experienced by patients as a significant side effect of treatment with rG-CSF, it would be desirable to provide a rG-CSF product that does not cause bone pain, either by means of a product that inherently does not have this effect or that is effective in a sufficiently small dose that no bone pain is caused. Thus, there is clearly a need for improved recombinant G-CSF molecules.
Protein-engineered variants of hG-CSF have been reported (U.S. Pat. No. 5,581,476, U.S. Pat. No. 5,214,132, U.S. Pat. No. 5,362,853, U.S. Pat. No. 4,904,584 and Riedhaar-Olson et al. Biochemistry 35: 9034-9041, 1996). Modification of hG-CSF and other polypeptides so as to introduce at least one additional carbohydrate chain as compared to the native polypeptide has also been reported (U.S. Pat. No. 5,218,092). In addition, polymer modifications of native hG-CSF, including attachment of PEG groups, have been reported and studied (see e.g., Satake-Ishikawa et al., (1992) Cell Structure and Function 17: 157; Bowen et al. (1999) Experimental Hematology 27: 425; U.S. Pat. No. 5,824,778, U.S. Pat. No. 5,824,784, WO 96/11953, WO 95/21629, and WO 94/20069).
The attachment of synthetic polymers to the peptide backbone in an attempt to improve the pharmacokinetic properties of glycoprotein therapeutics is known in the art. An exemplary polymer that has been conjugated to peptides is poly(ethylene glycol) (“PEG”). The use of PEG to derivatize peptide therapeutics has been demonstrated to reduce the immunogenicity of the peptides. For example, U.S. Pat. No. 4,179,337 (Davis et al.) discloses non-immunogenic polypeptides such as enzymes and peptide hormones coupled to polyethylene glycol (PEG) or polypropylene glycol. In addition to reduced immunogenicity, the clearance time in circulation is prolonged due to the increased size of the PEG-conjugate of the polypeptides in question.
One mode of attachment of PEG (and its derivatives) to peptides is a non-specific bonding through a peptide amino acid residue (see e.g., U.S. Pat. No. 4,088,538 U.S. Pat. No. 4,496,689, U.S. Pat. No. 4,414,147, U.S. Pat. No. 4,055,635, and PCT WO 87/00056). Another mode of attaching PEG to peptides is through the non-specific oxidation of glycosyl residues on a glycopeptide (see e.g., WO 94/05332).
In these non-specific methods, poly(ethyleneglycol) is added in a random, non-specific manner to reactive residues on a peptide backbone. Of course, random addition of PEG molecules has its drawbacks, including a lack of homogeneity of the final product, and the possibility for reduction in the biological or enzymatic activity of the peptide. Therefore, for the production of therapeutic peptides, a derivitization strategy that results in the formation of a specifically labeled, readily characterizable, essentially homogeneous product is superior. Such methods have been developed.
Specifically labeled, homogeneous peptide therapeutics can be produced in vitro through the action of enzymes. Unlike the typical non-specific methods for attaching a synthetic polymer or other label to a peptide, enzyme-based syntheses have the advantages of regioselectivity and stereoselectivity. Two principal classes of enzymes for use in the synthesis of labeled peptides are glycosyltransferases (e.g., sialyltransferases, oligosaccharyltransferases, N-acetylglucosaminyltransferases), and glycosidases. These enzymes can be used for the specific attachment of sugars which can be subsequently modified to comprise a therapeutic moiety. Alternatively, glycosyltransferases and modified glycosidases can be used to directly transfer modified sugars to a peptide backbone (see e.g., U.S. Pat. No. 6,399,336, and U.S. Patent Application Publications 20030040037, 20040132640, 20040137557, 20040126838, and 20040142856, each of which are incorporated by reference herein). Methods combining both chemical and enzymatic synthetic elements are also known (see e.g., Yamamoto et al. Carbohydr. Res. 305: 415-422 (1998) and U.S. Patent Application Publication 20040137557 which is incorporated herein by reference).
In response to the need for improved therapeutic G-CSF, the present invention provides a glycopegylated G-CSF that is therapeutically active and which has pharmacokinetic parameters and properties that are improved relative to an identical, or closely analogous, G-CSF peptide that is not glycopegylated. Furthermore, the invention provides methods for increasing hematopoiesis in a subject, particularly a subject who has received or will receive radiation or chemotherapy treatment.